This invention relates to valves and, more particularly, to valves of the type including a valve member journalled for rotation within a valve body through about 90.degree. between open and closed positions as, for example, a butterfly valve; and an inexpensive structure whereby a positive, corrosion resistant seal may be obtained.
Economic considerations in the fabrication of rotary valves such as butterfly valves, ball valves, etc., have resulted in a variety of proposals of structures whereby a valve member, such as a valve disc in a butterfly valve, can provide a good seal when in a closed position within a valve body without requiring expensive machining operations on the valve member when the same is formed of an extremely hard material as, for example, cast iron. More particularly, it will be recognized that the sealing surface on a valve member must be smooth and continuous so as to insure a positive seal against the valve seat. Since cast iron does not possess extremely good corrosion resistant properties, the two problems of economical construction and corrosion resistance have been solved by securing a hoop of corrosion resistant material to the valve member, which hoop defines a sealing surface on the valve member itself.
This approach is exemplified in U.S. Pat. No. 3,144,040 to White, among others, and has been successful to the extent that a valve that is not easily deteriorated by corrosion and which can be fabricated at a lesser cost than a variety of other valves has resulted.
Nonetheless, this approach still requires machining operations on the stainless steep hoop employed or complicated forming operations to obtain a proper cross sectional shape for the hoop, or both.